The field of the invention is electrolytic coating processes from a fused bath and apparatus therefore. The invention is particularly concerned with using a porous, hollow carbon anode in a fluoride melt in order to reduce the concentration of oxygen and thereby obtain improved niobium coatings.
The state of the art of electrolytic deposition from a fluoride melt may be ascertained by reference to copending U.S. Pat. 3,979,267, U.S. Pat. No. 3,444,058 of Mellors et al, and the Publication of Mellors et al in the Journal of the Electrochemical Society, Vol. 112, No. 3, Mar. 1965.
The state of the art of the carbon electrodes useful in the present invention (modified by drilling a hole lengthwise therein) may be ascertained by reference to the 1970 Canadian Catalog of Fisher Scientific Co., Limited, p. 172, particularly National AGKSP graphite electrodes, and the book "Ceramics for Advanced Technologies," by J. E. Hove and W. C. Riley (1965), published by John Wiley & Sons, pp. 14-25, particularly p. 21. The density of the National AGKSP electrodes is about 1.58 g/cm.sup.3. The material is composed of tiny crystallites of graphite, as shown on page 21 of the Hove and Riley book, and each crystallite is about 2.2 g/cm.sup.3. From Table 2.2 on page 22 of Hove and Riley, it can be determined that the graphite is composed of fine grained stock with a maximum particle size of the order of 0.015 inches.